U.S. Pat. No. 4,761,226, assigned to the assignee of the present invention, discloses a media filter filtration apparatus having an upper filter tank. The upper tank includes an imperforate end wall and a perforate floor provided with a lower filtrate compart-ment covered with a filter media. The lower compartment is connected to the intake of a pump. The filter media, either a paper web or a fibrous filter aid, is supplied from a roll or spool of the media and moved downwardly along an end wall of the tank and across the floor where the media is pulled by a chain and slat conveyor. The filter media is indexed, that is moved, and subsequently removed, when contaminated by advancing the conveyor after any vacuum is relieved.
Typically, the chain and slat conveyor follow fixed shoes or wheels around a rear radius path adjacent the imperforate end wall. Normal tolerances associated with the conveyor prevent it from being held tightly against the filter media, end wall and floor. A take-up mechanism may be operated in connection with the indexing of the media to take-up the contaminated filter media.
In this arrangement, particulate in the dirty liquid get between the end wall of the tank and filter media and are free to be received into the lower filtrate compartment through the perforate floor of the tank. These particles contaminate the filtrate, reducing the performance and efficiency of the filtering device.
During start-up and replacement of media rolls, old media is torn in several places and knotted together with a replacement roll of filter media. The knotted section must make its way to the discharge side of the apparatus before integrity of the filter is restored.